Principle terms

3 Insertion Diameter The diameter quoted as the actual diameter inserted into the anatomy of endoscope sheath

4 Instrument Axis The axis of the instrument relative to the instrument axis

5 Optical Axis The axis of the optical path which is displaced to the instrument axis

6 Angle of View The agular value of displacement to the optical axis

7 Optical Field of View The area which the conical system covers is as a cone

8 Fibre Illumination The area which the fibre illumination covers as a cone and is greater than the optical field of view

9 Working Length The actual length embodying the insertion diameter which can be applied

10 Light Post Input point of the illumination when connected to a light guide and source

11 Eyeshield Used as a cup for the eye or a diameter for the attachment of video camera equipment

Important Points.

When considering the diameters of endoscopes and sheaths and other instruments the diameters specified should be the external or outside diameter and not the bore or inside dimension.

As an example the 5.50mm of an Arthroscopic sheath (16.50Ch) should be a reference to the outside dimension of the shaft. Some confusion has occurred in the past with high flow sheaths with the inside or bore diameters specified.

Technical Notes

* Originally designed for use with the eye, the eyeshield is now used to fit a camera via an optical "coupler".

For glass on glass the eye-shield and sub-assembly is replaced with a unique fitting which dedicates the endoscope to a particular manufacturers camera product.

The axis positions shown will vary depending on the Angle of View of the endoscope and this variance is due in part to the illumination fibre position in the main outer tube.

Examples of terms used along with an illustration of the difference between "Portal View" and "Full Screen" images.

Generally, as the magnification increases, the "brightness" decreases - therefore the overfill on the CCDs is normally used in conjunction with large diameter endoscopes

Image via the endoscope fits within the vertical height of the CCDs for a given field size

Using the same field, the image over-fills the horizontal width of the CCDs by increasing the magnification of the image.

As most cameras today use CCD's (Charged Coupled Device) as the image scanning device the Eyepiece pupil via the eyepiece lens and the endoscope camera coupler will determine the size of the image contained within a diameter. The diameter is formed by the image fitting within the vertical height of the CCD active face.

The full screen versions have an image diameter that overfills the rectangular CCD active face forming a full screen monitor image. Full screen images have traditionally relied on large quantities of light via the optics such as 10.00mm diameter Laparoscopes etc., but new CCD technology creating reduced chip sizes have enabled smaller diameter endoscopes to fill the screen.

Fault Finding Endoscopes

The most common types of damage to the smaller diameter endoscopes tends to be broken relay optics.

Distal damage to the metal shaft that houses the optics and fibre illumination and broken & stained distal windows.

Shaft damage varies between endoscope type and therefore procedure.

Diathermy Loop Damage (Cystoscopy/Hysteroscopy) where the exposed portion of the electrode (loop) has made contact with the metal shaft and melted or fused the tube. Such damage can expose the illumination fibre and can breach the distal seal around the window allowing the instrument to leak.

Section drawing of a typical rod lens endoscope

Hopkins Rod Lens

The rod lens accounts for the relay section of the assembly.

The eyepiece can change the image size presented to the camera or eye.

The negative lens gives the field of view of the instrument.

Impact damage caused by dropping the endoscope onto a hard surface cracking the distal window or in some instances where power tools (e.g. used in Arthroscopy) make contact with the window surface. Most manufactures now employ synthetic sapphire being a very hard material in the hope that it is more durable than conventional optical glass and less liable to suffer this type of damage.

With the integrity of the window impaired a leak will occur allowing saline etc. to enter the optic assembly staining the lenses and in some instances breaking down the cement (adhesive) between the optical surfaces. If the window seal is breached during use or general handling and then placed say in an autoclave the optic assembly will probably fail leading to a significant repair or replacement charges.

All endoscope should be checked out at each end (proximal and distal) before they are placed in any form of cleaning, sterilizing or disinfections system.

The move towards minimally invasive surgical procedure has brought about a host of different of diagnosing and treating many conditions using scopes.
There are 2 main types of surgical scopes:
Rigid...